Use of water injection for promoting uniform initiation of underground combustion



Dec. 29, 1964 H. GREKEL 3,163,216

USE OF WATER INJECTION FOR PROMOTING UNIFORM INITIATION 0F UNDERGROUND COMBUSTION Filed Dec. 15, 1961 RADIUS OF TAR SAND SECTION HEATED FROM 50 F TO TEMPERATURE SHOWN USING ONE MILLION B.T.U. PER FT. FORMATION THICKNESS.

E 4 o N o I 5 a I LL 0 m 2 o 2 m O 500 I000 I500 2000 2500 TAR SAND TEMPERATURE, "F

HOWARD GREKEL INVENTOR.

ATTORNEY.

3,163,216 Patented Dec. 29, 1964 3,153,216 Uil 91? WATER lNlEtITlQN FOR PRGMOTENG UNH ORM ENTHATION F UNDERGROUND COMBUSTIGN Howard Greirel, Tulsa, Okla, assignor to Pan American Petroleum 0Tp03fi0n, Tulsa, Okla, a corporation: 0 Delaware 1 Filed Dec. 15, 1961, Ser. No. 159,5?1

- 9 Claims. ,(Cl. 166-11) The present invention relates to an improved method for conducting underground combustion of carbonaceous materials. More specifically, it is concerned with a novel means'of forming an initial burning zone involved in a reverse combustion process.

Diificulties frequently occur in establishing a reverse combustion burning front immediately after ignition because of uneven heating during ignition or cooling during the process of preparing the well for production. Once ignition has been established, the burner or other means employed is removed from the well and the well made ready to produce fluids. During the ignition step the formation pressure has usually built up to a substantial level, e.g., 700 to 900 psi. as a result of air injection via the injection well before and during the ignition step. To prevent the well from blowing in before it is ready for production, water or crude oil is circulated in the well bore to temporarily kill the well. While such measures accomplish the desired object of preventing the well from blowing in, they often-times extract so much heat away from the burning zone that when the well is placed on production and air injection is resumed, combustion cannot be established. Under such circumstances the formation must be reignited, and the chore of putting the Well on production again attempted.

It is, accordingly, an object of my invention to provide a method for establishing a uniform heated zone of adequate size around the well in initiating a reverse combustion process. It is another object to provide a method to diffuse the heat injected, or generated during ignition, over a larger volume of formation near the well and heating said formation to a slightly lower temperature level than the burning front, thereby rendering the heated zone more stable and less likely to be lost through cooling by the water circulation and production in the well during turn-around operations. 7 It is-still a further object of my invention to provide a method by which the zone around the producing well is heated to a substantially uniform temperature prior to placin said well on production, i.e., before reverse combustion.

In carrying out the process of my invention, a taror oil-bearing zone is first ignited by any one of several known methods. Generally, the thickness of the zone to be burned may range from about to feet, however, this dimension may be more or less than these values and the principles of my invention still be used to advantage. The ignition step should supply a quantity of sensible heat to the formation with the injected gas, typically at least 700,000 Btu. per foot of sand thickness. Generally, it is preferable not to consider the ignition step completed until the temperature of the formation adjacent the well has reached a temperature of at least about 1,000 to about l,500 F.

After ignition, water is injected into the burning zone via the production .well. The steam and hot water thus formed advance from the production well and beyond the burning zone. The hot zone is cooled to the boiling point of water and the cold formation beyond heated to the boiling point of water at the formation pressure. The temperature of the formation is raised substantially over a larger volume than occupied by the burning zone immediately after ignition. In this connection, the plot tion well.

shown in the accompanying drawing illustrates the effect of temperature level of the added heat on the radius of the heated zone around the well bore. Thus, it is seen that as the temperature level of the total heat added increases, the radius of the affected zone decreases. Temperatures generally above about 1,500 F. are usually higher than that of the injected gas and therefore represent temperaturelevels corresponding to heat generated in the formation. 7 I

Injection of water into the hot formation under the above conditions not only enables one to transmit heat to a greater volume of the formation, but the volume affected is more uniform in its dimensions. This is for the reason that the injected water initially tends to flow into the more permeable zones which are at a higher temperature since greater quantities of injected air enter such zones. As a result, higher steam pressures are generated in the hotter zones, causing remaining hot water and steam to flow into cooler zones of lower pressure, which may be either above or below the zones containing steam at higher pressure. The formation pressure should be high enough to maintain the steam condensation temperature at a high level for easy ignition. For example, at 695 p.s.i.g., the temperature Would-be about 500? F. and at'263 p.s;i.g. about 400 F., over which range combustion can be effected rather readily. The steam, of course, will condense Wherever it reaches formations at a temperature below its condensation temperature at that pressure, therefore automatically setting up pressure gradients in the desired direction towards cooler formations. Because of this pressure gradient, steam and hot water penetrate the formation throughout its thickness in relatively uniform fashion. This result is important because a larger volume of the formation has been elevated to a relatively high temperature, e.g., 500 F. at 695 p.s.i.g. On subsequent turn-around operations to put the well on production, the heated formation will not be appreciably cooled down except for a small area around the well When'oil' or water is circulated in the production well to temporarily kill it. The percentage of the heat lost by cooling near the well will be much smaller than Without the water addition because the heat hasbeen' diffused outwardly from the well. The heat will, therefore, be available so that combustion-can be resumed on further introduction of air via Thus, it will be seen that the formation in the vicinity of the well bore treated in accordance with my invention, owing to the fact that it is more uniformly heated in both its vertical and horizontal dimensions, provides more uniform initiation of reverse combustion than was possible by former procedures.

One of the surprising features of my invention is that the injection of water directly into the formation imme-' diately after the latter has been ignited does not extinguish combustion but, on the contrary, serves to diffuse the heat over a larger volume of the formation. The temperatures of the formation after the injection of water is lower than that of the initially heated burning zone, but covers a larger area. This renders the heated zone less susceptible to a drop in temperature below that required to sustain combustion after water circulation and production in the well bore in preparing the well for production, as previously discussed.

The amount of water introduced in accordance with my invention may, of course, vary. However, in general, it should depend on the quantity of heat injectedduring the ignition step and the temperature level of that heat which, in turn, determine the temperature of the formation and the extent of the heated zone. Ordinarily, I would say that the ratio of water to total heat added to the'system range from about 1 barrel per million Btu.

the injeca a) of total heat at initial temperatures of about 1,000'F. to about 2.5 bbls. per. million B.t.u. of total heat at the jmaximum temperature generated in the reservoir up to the time of ignition. Within this defined range, for example, atan initial formation temperature of 1,500 F., the amount of water to .be injected prior to placing the well on production'would be about 1.65 bbls. per millionv B;t.u.'

of total heat added or generated in the formation up to the time of ignition. The total heat in a case of' this sort will be the heat added to the system; via the burner in igniting the formation plus I the heat generated from Q burning thenative hydrocarbons withexcess oxygen supplied from the ignition step. a

While the process of my invention finds special'applicationto tar sands and similarlunconsolidated) formations, it is equally applicable to other normally liquid hydrocarbon reservoirs, coal and oii shale deposits, and

the like; in which reverse or forward'cornbustion processes'fcan be used. Also, it should be pointed out that while :themetho'd of my invention is very useful in caseswhere a relatively high gas pressure exists in the reservoir "subsequent to ignitionbut priorto, production, this improvement can be applied with similar effectivenessto a formation having little or no gas pressure. For

example, heat may be supplied to the formation by means other than one utilizing a high build-up of oxygen in p the formation, such 'as a thermite bomb, arrelectrical After this step, however, it will heater, and the like. be necessary to inject gas, preferably containing oxygen, to raise. the formation pressure to a level'high enough to obtain the desired high steam condensation temperature, e.g., 400500 F. Water may then be injected through the resulting heated area and into the formation, thus allowing the heat to be more readily and thoroughly diffused back into the formation so that the zone around the well is heated to a uniform temperature.

Itwill'also be evident that while the foregoing dis-' cussion'has been directed primarily toward the use of my inventron in reverse combustion, it is likewise applicable With equal eifectiveness to forward combustion The term carbonac eous as used herein is intended to refer to materials comprising either free or combined carbon. I

I claim:

1. In a process for conducting combustion in an underground carbonaceous deposit penetrated Welland an injection well, i the improvement which comprises igniting said deposit adjacent one of said wells wherebythe temperature in the latter reaches a minimum level of about 1000 to aboutlSOO" F., injecting'an oxygencontaining gas into said deposit via. said. injection well to produce a pressure therein of at least about 260 p.s.i.g., 1' j a then injecting water into said one of said wells in an amount corresponding to from about 1 barrel per million B.t.u. of total heat at an initial formation temperature of about 1000 F. to about 2.5 barrels by a producing per million Btu; of total heat at the maximum temperature generated in said deposit up to the time of ignition whereby the volume of said deposit, at combustion supporting temperature in, the region of said producing, well increased and rendered more "uniform, both" horizontally and vertically, thereafter efiecting'rcombu'stion in said deposit by introducing a combustionsupporting gas down said injection well, and recovering fluid products from said producing well.

a a 3. In a process for conducting reverse combustion .in

' jection well whereby the temperature in. the latter reaches 2. In a process for conducting combustion in an underground carbonaceous deposit penetrated by a producing well and an injection well,

P the improvement which comprises igniting said de- 7 posit immediately adjacent one of said wells whereby the temperature in the latter reaches a minimum level of about "1 000 to. about 1500 F., injecting.

an oxygen-containing gas into said deposit via said injection Weil to produce a pressure therein of at least about 260 p.s.i.g.,

injecting water into said one of said wells in an amount corresponding to from about 1 barrel. per million Btu. of total heat at an initial formationtemperature of about 1000 F. toabout 2.5 barrels per million Btu. of total heat at the maximum temperature 3 generated in said deposit up to the time of ignition,

thereafter effecting combustion in said deposit by -in- :troducinga combustion supporting gas down said injection well, and recovering fluid products from one of said wells.

an underground carbonaceous deposit penetrated by a producing well and an injection well,

the improvement which comprises igniting said' deposit adjacent said producing well whereby the tem perature in the latter reaches a' minimum level of about 1000 to about 1500 F., injecting an oxygen containing gas into said deposit via said injection 7 wellto produce a pressure therein of at least about 260 p.s.i.g.,

next introducing water into said producing well in an amount corresponding to from about l barrel permillion B.t.u. of. total heat at an initial formation temperatureof. about 1000" F. to about.2.5 barrels per million Btu. of total heat at the maximum term:

i perature generated-in said deposit up to the time of 4. In a process for conducting forward combustion in an underground carbonaceous deposit penetrated by a producing well and an injection well, the. improvement which comprises igniting said deposit adjacent said in a minimum level of about l000 to about 1500 F., injecting an oxygen-containing gas into said deposit via said injection well-toproduce a pressure thereinof at least about 260 p.s.i.g., next introducing wateriinto said injection well million Btu. of total heat at an initial formation temperature of about 1000 F. to about 2.5 barrels per-million Btu. of total heat at the maximum tem-' perature generated in said deposit up tothe time of ignition,

thereafter effecting combustion in said deposit by in troducing a combustion supporting gas down said injection well, and recovering fluid products from 'said producing'well. 5. The process of claim 3 in which said deposit holds an oxygen-containing gas at a pressure of at least 700 p.s.i.g. as a result of injecting said oxygen-containing in an i amount corresponding to from about 1 barrel per i next introducing water into said producing well in an amount corresponding to from about 1 barrel per million B.t.u. of total heat at an initial formation temperature of about 1000 F. to about 2.5 barrels per million B.t.u. of total heat at the maximum temperature generated in said deposit up to the time of ignition,

whereby the volume of said deposit at combustion supporting temperature in the region of said producing well is increased and rendered more uniform both horizontally and vertically,

thereafter effecting combustion in said deposit by introdcing a combustion supporting gas down said injection well, and recovering fluid products from said producing Well. 7. In a process of conducting forward combustion in an underground carbonaceous deposit penetrated by at producing well and an injection well,

the improvement which comprises igniting said deposit immediately adjacent said injection well whereby the temperature in the latter reaches a minimum level of about lO00 to about 1500 F., injecting an oxygen-containing gas into said deposit via said injection well to produce a pressure therein'of a least about 260 p.s.i.g.,

next introducing water into said injection well in an amount corresponding to from about 1 barrel per million B.t.u. of total heat at an initial formation temperature of about lO00 F. to about 2.5 barrels per million B.t.u. of total heat at the maximum temperature generated in said deposit up to the time of ignition, whereby the volume of said deposit at combustion supporting temperature in the region of said injection well is increased and rendered more uniform 'both horizontally and vertically,

thereafter elfecting combustion in said deposit by introducing a combustion supporting gas down said injection well, and recovering fluid products from said producing well.

8. In a process for conducting reverse combustion in an underground carbonaceous deposit penetrated by a producing well and an injection well,

the improvement which comprises igniting said deposit immediately adjacent said producing well whereby the temperature in the latter reaches a minimum level of about 1000 to about 1500 F., injecting an oxygen-containing gas into said deposit via said injection well to produce a pressure therein of at least about 260 p.s.i.g.,

next introducing water into said producing well in an amount corresponding to from about 1 barrel per million B.t.u. of total heat at an initial formation temperature of about 1000 F. to about 2.5 barrels per million B.t.u. of total heat at the maximum temperature generated in said deposit up to the time of ignition,

whereby the volume of said deposit at combustion supporting temperature in the region of said producing well is increased and rendered more uniform both horizontally and vertically,

thereafter effecting combustion in said deposit by introducing a combustion supporting gas down said injection well, and recovering fluid products from said producing well. 9. 'In a process of conducting forward combustion in an underground carbonaceous deposit penetrated by a producing well and an injection well,

the improvement which comprises igniting said deposit immediately adjacent said injection well whereby the temperature in the latter reaches a minimum level of about lO00 to about 1500 F.,

injecting an oxygen-containing gas into said deposit via said injection well to produce a pressure therein of from about 260 to about 695 p.s.i.g.,

next introducing water into said injection well in an amount corresponding to from about 1 barrel per million B.t.u. of total heat at an initial formation temperature of about lO00 F. to about 2.5 barrels per million B.t.u. ofvtotal heat at the maximum temperature generated in said deposits up to the time of ignition,

whereby the volume of said deposit at combustion supporting temperature in the region of said injection well is increased and rendered more uniform both horizontally and vertically, thereafter effecting combustion in said deposit by introducing a combustion supporting gas down said injection well, and recovering fluid products from said producing Well.

References Cited in the file of this patent UNITED STATES PATENTS 2,780,449 Fisher et al. Feb. 5, 1957 0 2,788,071 Pelzer Apr. 9, 1957 3,055,423 Parker Sept. 25, 1962 

2. IN A PROCESS FOR CONDUCTING COMBUSTION IN AN UNDERGROUND CARBONACEOUS DEPOSIT PENETRATED BY A PRODUCING WELL AND AN INJECTION WELL, THE IMPROVEMENT WHICH COMPRISES IGNITING SAID DEPOSIT IMMEDIATELY ADJACENT ONE OF SAID WELLS WHEREBY THE TEMPERATURE IN THE LATTER REACHES A MINIMUM LEVEL OF ABOUT 1000* TO ABOUT 1500*F., INJECTING AN OXYGEN-CONTAINING GAS INTO SAID DEPOSIT VIA SAID AN OXYGEN-CONTAINING GAS INTO SAID DEPOSIT VIA SAID INJECTION WELL TO PRODUCE A PRESSURE THEREIN OF AT LEAST ABOUT 260 P.S.I.G., INJECTING WATER INTO SAID ONE OF SAID WELLS IN AN AMOUNT CORRESPONDING TO FROM ABOUT 1 BARREL PER MILLION B.T.U. OF TOTAL HEAT AT AN INITIAL FORMATION TEMPERATURE OF ABOUT 1000*F. TO ABOUT 2.5 BARRELS PER MILLION B.T.U. OF TOTAL HEAT AT THE MAXIMUM TEMPERATURE GENERATED IN SAID DEPOSIT UP TO THE TIME OF IGNITION, THEREAFTER EFFECTING COMBUSTION IN SAID DEPOSIT BY INTRODUCING A COMBUSTION SUPPORTING GAS DOWN SAID INJECTION WELL, AND RECOVERING FLUID PRODUCTS FROM ONE OF SAID WELLS. 